Light-emitting device and method for manufacturing light-emitting device

ABSTRACT

Techniques are provided for manufacturing a light-emitting device having high internal quantum efficiency, consuming less power, having high luminance, and having high reliability. The techniques include forming a conductive light-transmitting oxide layer comprising a conductive light-transmitting oxide material and silicon oxide, forming a barrier layer in which density of the silicon oxide is higher than that in the conductive light-transmitting oxide layer over the conductive light-transmitting oxide layer, forming an anode having the conductive light-transmitting oxide layer and the barrier layer, heating the anode under a vacuum atmosphere, forming an electroluminescent layer over the heated anode, and forming a cathode over the electroluminescent layer. According to the techniques, the barrier layer is formed between the electroluminescent layer and the conductive light-transmitting oxide layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/687,204, filed Mar. 16, 2007, now allowed, which is a continuation ofU.S. application Ser. No. 10/967,281, filed Oct. 19, 2004, now U.S. Pat.No. 7,205,716, which claims the benefit of a foreign priorityapplication filed in Japan as Serial No. 2003-359778 on Oct. 20, 2003,all of which are incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a light-emitting device and to a methodfor manufacturing the light-emitting device, in which each pixelcomprises a light-emitting element.

RELATED ART

Since a light-emitting element emits light by itself, it is highlyvisible and does not require a backlight that is needed in a liquidcrystal display device (LCD) and therefore the light-emitting element isbest suited for a thin device. Moreover, the light-emitting element hasa wider viewing angle than the LCD. For these reasons, attention hasbeen paid to a light-emitting device using the light-emitting element asan alternative display device to a CRT and the LCD, and it has beentried to put the light-emitting device to practical use. An OLED(Organic Light Emitting Diode), which is one of the light-emittingelements, has an anode, a cathode, and a layer (hereinafter referred toas an electroluminescent layer) including an electroluminescent materialwhere luminescence (electroluminescence) is obtained by applying anelectric field. The OLED emits light by combining a hole injected fromthe anode and an electron injected from the cathode in theelectroluminescent layer.

The work function of the material for forming the electrode is oneindicator to determine the hole-injecting property and theelectron-injecting property into the electroluminescent layer. It isdesirable to use the material having low work function as an electrode(cathode) on the side where the electron is injected and to use thematerial having high work function as an electrode (anode) on the sidewhere the hole is injected. Specifically, indium tin oxide (ITO) havinga work function of approximately 5 eV is usually used as the anode.

Since the light-emitting device does not use the backlight, the powerconsumption of the light-emitting device more likely to depend on theperformance of the light-emitting element of each pixel. That is to say,when the light-emitting element has higher external quantum efficiency(the number of photons extracted to the outside/the number of injectedcarriers), the less power consumption can be achieved. The externalquantum efficiency can be raised by increasing the light extractionefficiency (the number of photons extracted to the outside/the number ofemitted photons) or the internal quantum efficiency (the number ofemitted photons/the number of injected carriers). The increase of theinternal quantum efficiency means the decrease of the energy of the heatconverted from the electricity given to the light-emitting element.Therefore, it is considered that the increase of the internal quantumefficiency not only reduces the power consumption but also suppressesthe lowering of the reliability due to the heating.

As one factor to determine the internal quantum efficiency, an injectionbalance of the carrier (the proportion between the injected electron andthe injected hole) is given. The injection balance depends on the workfunction of the electrode, the work function of a layer among theelectroluminescent layer that contacts the electrode, and the mobilityof the carrier in the electroluminescent layer. The internal quantumefficiency can be raised as the injection balance approaches 1.

However, it is not easy to find out the combination of the material ofthe electrode and the material of the electroluminescent material thatcan enhance the injection balance, and it is difficult to obtainsufficient luminance in spite of its high power consumption in theconventional light-emitting element. Moreover, the conventionallight-emitting element has short half-life period of luminance and has aproblem to be solved concerning the reliability. Although it isnecessary that at least one electrode has light-transmitting property inorder to extract the light from the light-emitting element, the materialof the conductive light-transmitting film is limited and there are notmany choices. Many conductive light-transmitting films are formed ofITO, and when ITO is used as the anode, it is necessary to optimize thematerial of the layer that has hole-transporting property and thatcontacts the anode. However, the development of the new material costsmuch and takes much time.

BRIEF SUMMARY OF THE INVENTION

The present invention is made in view of the above problems and it is anobject of the present invention to provide a light-emitting device usinga light-emitting element having the high internal quantum efficiency,consuming less power, having high luminance, and having highreliability. Moreover, it is an object of the present invention toprovide a method for manufacturing such a light-emitting device.

The present inventors considered that the injection balance becomes poorbecause of the following reason. When a conductive layer including oxideand having light-transmitting property (hereinafter referred to as aconductive light-transmitting oxide layer: CTO) used as the anodecontacts a layer having a hole-transporting property (a hole-injectinglayer or a hole-transporting layer), the carrier moves so that Fermipotential corresponds. As a result, the energy band of thehole-injecting layer or the hole-transporting layer bends, and this bendprevents the hole-injecting property from improving and causes theinjection balance to become poor.

FIG. 2 shows a band model in the condition where a conductivelight-transmitting oxide layer contacts a hole-injecting layer (HIL).When the HIL does not contact the CTO, the Fermi potential is differentin the HIL and the CTO, and the HIL has the flat energy band. However,when the HIL contacts the CTO, the energy band in the HIL bends in adirection where the barrier is formed against the electron so that theFermi potential E_(F) corresponds, and the hole comes to strong in thevicinity of the interface between the CTO and the HIL as shown in FIG.2. For this reason, it is supposed that hole-injecting property and thehole mobility are suppressed, that the injection balance of the carrieris difficult to increase, and therefore that the increase of theinternal quantum efficiency is interrupted.

Consequently, in the present invention, a highly insulative layer(hereinafter referred to as a barrier layer) having the thickness ofsuch a degree that the tunneling current can flow is provided in aregion of the anode that is closest to the hole-injecting layer or thehole-transporting layer. The barrier layer is formed of the materialhaving higher resistance than the material of the layers in the anodeexcept for the barrier layer and the material of the layers (thehole-injecting layer or the hole-transporting layer) that has thehole-transporting property and that contacts the barrier layer. With theabove structure, the width of the energy band of the barrier layer canbe made broader than those of the conductive light-transmitting oxidelayer and the layer having the hole-transporting property. Specifically,in the present invention, the anode is formed of a conductivelight-transmitting oxide material, and the barrier layer correspondingto a part of the anode is formed of the silicon oxide and the conductivelight-transmitting oxide material or formed of a thin insulative orsemi-insulative material including the silicon oxide.

FIGS. 1A and 1B show a band model in the condition where the barrierlayer of the CTO contacts the HIL. The barrier layer includes thesilicon oxide and is insulative or semi-insulative. The barrier layer isformed in the thickness of such a degree that the carrier can betunneled, which is from 0.5 to 5 nm. By forming the barrier layer, theCTO and the HIL can be isolated physically. Thus, even when the Fermipotential E_(F) corresponds in the CTO, the barrier layer, and the HILas shown in FIG. 1A, the energy band of the CTO is flat. Therefore,since the hole-injecting property is improved and since the holemobility is enhanced, the injection balance of the carrier can beenhanced. As a result, the internal quantum efficiency can be enhancedaccordingly.

The energy band of the HIL is not always flat completely as shown inFIG. 1A, and it may bend in a direction where the energy is low as shownin FIG. 1B. However, unlike the bend of the energy band shown in FIG. 2,the bend of the energy band shown in FIG. 1B acts so as to interrupt thestorage of the hole. As a result, since the hole-injecting property isimproved and since the hole mobility is enhanced, the injection balanceof the carrier is enhanced, and the internal quantum efficiency can beraised accordingly.

It is noted that the silicon oxide has the characteristic that itadsorbs the water molecule easily by chemical bonding. Therefore, it isconsidered that the CTO including the silicon oxide adsorbs the moistureon its surface more easily than the general CTO. FIGS. 3A and 3B showthe quantity of gas exhausted from the substrate with respect to thetemperature that is measured by a TDS (Thermal Desorption Spectroscopy)method. The substrate is in the condition where the anode is formedthereover but the layer having the hole-transporting property is notformed yet.

FIG. 3A shows the quantity of the exhausted gas with respect to thetemperature when the silicon oxide and the ITO are used as the anode.FIG. 3B shows the quantity of the exhausted gas with respect to thetemperature when the ITO is used as the anode. In both FIGS. 3A and 3B,after forming the anode, a heat treatment is performed for an hour at atemperature of 200° C. under the atmosphere. In the substrate used inFIG. 3A, the composition of the anode is O:Si:In:Sn=61:3:34:2.

In FIGS. 3A and 3B, the horizontal axes indicate the temperature of theheater used in the heat treatment. The actual temperature of thesubstrate is lower than the temperature of the heater and this tendencyis more remarkable when the temperature of the heater is higher.

In both substrates used in FIGS. 3A and 3B, the peak showing thedesorption of the water physically adsorbed is observed at a temperatureof approximately 120° C. (the temperature of the substrate is alsoapproximately 120° C.) as indicated by the horizontal axes of FIGS. 3Aand 3B. However, unlike when only the ITO is used as the anode, when thesilicon oxide and the ITO are used as the anode as shown in FIG. 3A, thepeak showing the desorption of the water is observed again at thetemperature ranging from approximately 350 to 370° C. (the temperatureof substrate ranging from approximately 300 to 320° C.). It isconsidered that the peak observed at temperature ranging form 350 to370° C. indicates the desorption of the moisture adsorbed on the siliconoxide by chemical bonding.

The above result of measurement by the TDS indicates that the barrierlayer including the silicon oxide adsorbs the moisture on its surfacemore easily than the barrier layer including only the CTO. When thesurface of the anode is contaminated by the moisture or the like, thework function lowers and therefore the hole-injecting propertydeteriorates. Therefore, the injection balance becomes poor, and theinternal quantum efficiency lowers accordingly. Moreover, the moistureadsorbed on the surface of the anode may cause the deterioration of theelectroluminescent layer.

Consequently, in the present invention, after forming the anode havingthe barrier layer and before forming the layer having thehole-transporting property, a heat treatment is performed under theatmosphere or a heat treatment (vacuum bake) is performed under thevacuum atmosphere to the anode in order to remove the moisture adsorbedon the surface of the barrier layer. With the above structure, it ispossible to prevent the injection balance of the carrier from becomingpoor and the reliability from lowering due to the moisture adsorbed onthe barrier layer.

It is noted that the electroluminescent layer includes a plurality oflayers in the present invention. These layers can be classified into ahole-injecting layer, a hole-transporting layer, a light-emitting layer,an electron-transporting layer, an electron-injecting layer, and thelike in point of the carrier-transporting property. The hole-injectinglayer and the hole-transporting layer are not always distinguishedstrictly and they are the same in point of that the hole-transportingproperty (the hole mobility) is important. In this specification,, thelayer contacting the anode is referred to as the hole-injecting layerand the layer contacting the hole-injecting layer is referred to as thehole-transporting layer for convenience. In the same way, the layercontacting the cathode is referred to as the electron-injecting layerand the layer contacting the electron-injecting layer is referred to asthe electron-transporting layer. Sometimes the light-emitting layer alsoworks as the electron-transporting layer and therefore it is alsoreferred to as a light-emitting electron-transporting layer.

The electroluminescent layer may be formed of not only the organicmaterial but also the material in which an organic material and aninorganic material are combined or the material in which a metal complexis added to the organic material when the same function is obtained.

The interface between the barrier layer and the conductivelight-transmitting oxide layer is not always necessary to be clear. Forexample, the interface therebetween may change gradually so that theconcentration of the oxide in the anode is higher toward theelectroluminescent layer. Although the interface between the barrierlayer and the conductive light-transmitting oxide layer is not clear inthis case, the region closer to the electroluminescent layer still worksas the barrier layer.

In the present invention described above, the conductivelight-transmitting oxide layer can be formed of another conductivelight-transmitting oxide material such as indium tin oxide (ITO), zincoxide (ZnO), indium zinc oxide (IZO), or gallium-doped zinc oxide (GZO).It is preferable that the anode is formed by a sputtering method using atarget including the conductive light-transmitting oxide material andthe silicon oxide.

Advantageous Effect of the Invention

In the present invention, the hole-injecting property can be improvedand the hole mobility can be enhanced by forming the barrier layer. As aresult, the injection balance of the carrier can be enhanced and theinternal quantum efficiency can be raised accordingly. Moreover, sincethe layer having the hole-transporting property is formed after removingthe moisture adsorbed on the silicon oxide included in the barrier layerby the vacuum bake, it is possible to prevent the lowering of thehole-injecting property and to prevent the deterioration of theelectroluminescent layer due to the moisture. Therefore, the presentinvention can provide a light-emitting element consuming less power,having high luminance, and having high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are drawings of a band model to explain the state inwhich an insulative or semi-insulative barrier film including silicon orsilicon oxide is formed at the interface between the conductivelight-transmitting oxide layer and the hole-injecting layer;

FIG. 2 is a drawing of a band model for showing the contact condition ofthe conventional conductive light-transmitting oxide layer and thehole-injecting layer;

FIGS. 3A and 3B are graphs for showing the result of the measurement ofTDS;

FIGS. 4A and 4B are drawings for showing a structure of thelight-emitting element in the light-emitting device of the presentinvention;

FIGS. 5A to 5C are drawings for showing the manufacturing method of thelight-emitting device of the present invention;

FIGS. 6A and 6B are drawings for showing the manufacturing method of thelight-emitting device of the present invention;

FIGS. 7A and 7B are cross-sectional views of the light-emitting devicemanufactured by the present invention;

FIG. 8 is a cross-sectional view of the light-emitting devicemanufactured by the present invention;

FIGS. 9A to 9C are circuit diagrams of the pixel of the light-emittingdevice;

FIG. 10A is a top view of the light-emitting device;

FIGS. 10B to 10F are circuit diagrams of the protective circuit;

FIG. 11A is a top view of the light-emitting device of the presentinvention;

FIG. 11B is a cross-sectional view of the light-emitting device of thepresent invention;

FIGS. 12A to 12C are drawings of the electronic equipments of thelight-emitting device;

FIGS. 13A and 13B are cross-sectional views of the light-emitting deviceof the present invention; and

FIGS. 14A to 14C are graphs for showing the measured value of thecurrent efficiency of the luminance.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment mode of the present invention is hereinafter explained.The light-emitting element of the present invention has anelectroluminescent layer provided between an anode formed of theconductive light-transmitting oxide material and of the silicon oxideand a cathode including alkali metal or alkali-earth metal. Theelectroluminescent layer is formed by laminating layers including thelight-emitting organic compound. The layers including the organiccompound can be classified into a hole-transporting layer, alight-emitting layer, and an electron-transporting layer according toits carrier-transporting property. Moreover, a hole-injecting layer maybe provided between the anode and the hole-transporting layer, and anelectron-injecting layer may be provided between the cathode and theelectron-transporting layer. The distinction between the hole-injectinglayer and the hole-transporting layer and between the electron-injectinglayer and the electron-transporting layer is not strict and they are thesame in point of that the hole-transporting property (the hole mobility)or the electron transporting property (the electron mobility) isimportant. In addition, a hole-blocking layer may be provided betweenthe electron-transporting layer and the light-emitting layer. Thelight-emitting layer may emit the light of various colors by adding aguest material such as pigment or a metal complex to a host material. Inother words, the light-emitting layer may be formed using a luminescencematerial or a phosphorescence material.

The anode is formed of the material in which the silicon oxide is addedin the range of 1 to 10 atomic % to the conductive light-transmittingoxide material selected from the group consisting of indium tin oxide(ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and gallium-doped zincoxide (GZO). In a region of the anode that contacts theelectroluminescent layer, a barrier layer that is insulative orsemi-insulative and in which the density of the silicon is higher thananother region in the anode is provided. The barrier layer has thethickness of such a degree that the carrier can move from the anode tothe electroluminescent layer, which means the thickness of such a degreethat the current flows by the tunneling current. The barrier layerseparates physically the electroluminescent layer and the conductivelight-transmitting oxide layer that is a part of the anode and thatcontacts the barrier layer, and this makes it possible for the carrierto move.

The anode including the conductive light-transmitting oxide material canbe formed by the sputtering method using the target including theconductive light-transmitting oxide material and the silicon oxide. Thecontent ratio of the silicon oxide to the conductive light-transmittingoxide material in the target may be in the range of 1 to 20 wt. %,preferably in the range of 2 to 10 wt. %. The content ratio of thesilicon oxide may be determined in the above range appropriately becausethe anode has high resistance when the density of silicon oxide isincreased in the above range. This provides the anode including thesilicon oxide in the range of 1 to 10 atomic %, preferably in the rangeof 2 to 5 atomic %, and the conductive light-transmitting oxidematerial. When the same composition can be obtained, the anode may beformed by co-evaporation using the vacuum deposition method. The termco-evaporation refers to an evaporation method that evaporation sourceand heated simultaneously and different materials are mixed together atthe deposition step.

The barrier layer can be formed in such a way that the conductivelight-transmitting oxide material in the surface course of the anodeincluding the silicon oxide and the conductive light-transmitting oxidematerial is removed so that the density of the silicon is higher thanthat of the conductive light-transmitting oxide material in the surfacecourse of the anode. For example, the barrier layer can be formed by amethod in which the surface is processed using a solution that canremove the conductive light-transmitting oxide material selectively; aplasma process using one or a plurality of gases selected from the groupconsisting of hydrogen, oxygen, and hydrofluoric acid; a plasma processusing an inert gas such as nitrogen or argon; or the like.

In the case of changing the surface course of the anode into the barrierlayer by removing the conductive light-transmitting oxide material fromthe surface course of the anode, it is preferable that the barrier layeris formed roughly at the submicron level to some extent because thebarrier film is difficult to be formed when the conductivelight-transmitting oxide layer is formed at high density. With the abovestructure, when the conductive light-transmitting oxide material isremoved selectively, it is possible to increase the density of the addedsilicon efficiently in comparison with that of the conductivelight-transmitting oxide material.

The barrier layer may be formed by increasing the density of the siliconin the region of the conductive light-transmitting oxide layer that isclose to the surface intentionally when forming the conductivelight-transmitting oxide layer. Specifically, a barrier layer may beformed in such a way that after forming the conductivelight-transmitting oxide layer, the barrier layer in which the weightpercentage of the silicon is higher may be formed newly on theconductive light-transmitting oxide layer formed previously by changingthe composition of the target used in the sputtering so that the densityof the silicon becomes higher.

In the present invention, before forming the electroluminescent layer, aheat treatment is performed to the anode under the atmosphere or thevacuum atmosphere (preferably at the pressure in the range ofapproximately 10⁻⁴ to 10⁻⁸ Pa) at temperature of the substrate rangingfrom 200 to 450° C., preferably from 250 to 300° C. Moreover, a washingprocess or a polishing process may be performed in order to clean and toenhance the flatness.

In the light-emitting element having the above structure, an originaladvantageous effect of the work function of the anode can be obtainedbecause the anode and the hole-injecting layer or the hole-transportinglayer do not contact each other. In other words, the hole injectionefficiency to the hole-injecting layer can be raised and the injectionbalance can be enhanced. As a result, the internal quantum efficiencycan be raised.

FIG. 4A shows the structure of the light-emitting element obtained bythe present invention. The light-emitting element shown in FIG. 4A hasan anode 101 formed on a substrate 100, an electroluminescent layer 102formed on the anode 101, and a cathode 103 formed on theelectroluminescent layer 102.

The anode 101 has a barrier layer 109 a and a conductivelight-transmitting oxide layer 109 b. The barrier layer 109 a is betweenthe conductive light-transmitting oxide film 109 b and theelectroluminescent layer 102.

The cathode 103 can be formed of metal, alloy, conductive compound, orthe mixture of these each of which has low work function and is usuallyused as the cathode of the light-emitting element. Specifically, thecathode can be formed of alkali metal such as Li or Cs; alkali-earthmetal such as Mg, Ca, or Sr; alloy including these such as Mg:Ag orAl:Li; or rare-earth metal such as Yb or Er. When the layer includingthe material having high electron-injecting property is formed so as tocontact the cathode 103, the general conductive film using aluminum,conductive light-transmitting oxide material, or the like can be used asthe cathode 103.

In FIG. 4A, the electroluminescent layer 102 has first to fifth layers104 to 108.

Since the first layer 104 formed on the barrier layer 109 a works as thehole-injecting layer, it is desirable that the first layer 104 is formedof the material having hole-transporting property, having comparativelylow ionization potential, and having high hole-injecting property. Thematerial is classified broadly into metal oxide, low-molecule organiccompound, and high-molecule organic compound. As the metal oxide, forexample, vanadium oxide, molybdenum oxide, ruthenium oxide, or aluminumoxide can be used. As the low-molecule organic compound, for example,starburst amine typified by m-MTDATA, metallo phthalocyanine typified bycopper phthalocyanine (abbreviation Cu-Pc), phthalocyanine (abbreviationH₂-Pc), 2,3-dioxyethylenethiophene derivative can be used. Moreover, afilm formed by co-evaporating the low-molecule organic compound and theabove metal oxide may be used. As the high-molecule organic compound,for example, polymer molecule such as polyaniline (abbreviation PAni),polyvinylcarbazole (abbreviation PVK), or polythiophene derivative canbe used. Polyethylenedioxythiophene (abbreviation PEDOT), which is oneof the polythiophene derivatives, with polystyrenesulfonic acid(abbreviation PSS) doped may be used. Moreover, benzoxyazole derivativemay be used in combination with one or a plurality of materials selectedfrom the group consisting of TCQn, FeCl₃, C₆₀, and F₄TCNQ.

It is preferable that the second layer 105 formed on the first layer 104is made of the known material having high hole-transporting property andhaving low crystallinity because the second layer 105 works as thehole-transporting layer. Specifically, the aromatic amine compound(which means the material having nitrogen-benzene ring bond) such as4,4-bis[N-(3-methylphenyl)-N-phenyl-amino]biphenyl (abbreviation TPD),its derivative 4,4′-bis[N-(1-naphtyle)-N-phenyl-amino]biphenyl(abbreviation α-NPD), and the like are given. Moreover, a starburstaromatic amine compound such as4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation TDATA) orMTDATA can be used. Furthermore,4,4′,4″-tris(N-carbazolyl)triphenylamine (abbreviation TCTA) can beused. As the high-molecule material, poly vinylcarbazole showing goodhole-transporting property can be used.

It is preferable that the third layer 106 formed on the second layer 105is formed of the material having high ionization potential and largeband gap because the third layer 106 works as the light-emitting layer.Specifically, for example, metal complex such as tris(8-quinolinolato)aluminum (abbreviation Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbreviation Almq₃),bis(10-hydroxybenzo[η]-quinolinolato)beryllium (abbreviation BeBq₂),bis(2-methyl-8-quinolinolato)-(4-hydroxy-biphenylyl)-aluminum(abbreviation BAlq), bis[2-(2-hydroxyphenyl)-benzooxazolate]zinc(abbreviation Zn (BOX)₂), orbis[2-(2-hydroxyphenyl)-benzothiazolate]zinc (abbreviation Zn(BTZ)₂) canbe used. Moreover, luminescent pigment (for example, coumarinderivative, quinacridone derivative, rubrene, 4,4-dicyanomethylene,1-pyrone derivative, stilbene derivative, condensed aromatic compound,and the like) can be used. Furthermore, phosphorescent material such asplatinum octaethylporphyrin complex, tris(phenylpyridine)iridiumcomplex, or tris(benzylidyneacetonato)phenanthreneeuropium complex canbe used.

As the host material of the third layer 106, the hole-transportingmaterial or the electron-transporting material typified by the aboveexample can be used. Moreover, a bipolar material such as4,4′-N,N′-dicarbazolylbiphenyl (abbreviation CBP) can be used.

It is desirable that the fourth layer 107 formed on the third layer 106is formed of the material having high electron-transporting propertybecause the fourth layer 107 works as the electron-transporting layer.Specifically the metal complex having quinoline skeleton orbenzoquinoline skeleton typified by Alq₃ or its mixed ligand complex canbe used. Specifically, the metal complex such as Alq₃, Almq₃, BeBq₂,BA1q, Zn(BOX)₂, or Zn(BTZ)₂ can be given. Moreover, not only the metalcomplex but also oxadiazole derivative such as2-(4-biphenylyl)-5-(4-tert-buthylphenyl)-1,3,4-oxadiazole (abbreviationPBD) and 1,3-bis[5-(p-tert-buthylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviation OXD-7); triazole derivative such as3-(4-tert-buthylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation TAZ) and3-(4-tert-buthylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation p-EtTAZ); an imidazole derivative such as TPBI; andphenanthroline derivative such as bathophenanthroline (BPhen) andbathocuproine (BCP) can be used.

It is desirable that the fifth layer 108 formed on the fourth layer 107is formed of the material having high electron-injecting propertybecause the fifth layer 108 works as the electron-injecting layer.Specifically, the fifth layer 108 is often formed of a very thin filmmade of the insulator such as alkali metal halide such as LiF or CsF;alkali-earth metal halide such as CaF₂; or alkali metal oxide such asLi₂O is often used. Moreover, alkali metal complex such as lithiumacetylacetonate (abbreviation Li(acac)) or 8-quinolilato-lithium(abbreviation Liq) is also effective. In addition, the fifth layer 108may include benzoxazole derivative or the metal oxide such as molybdenumoxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx), or tungstenoxide (WOx) with one or a plurality of materials selected from the groupconsisting of alkali metal; alkali-earth metal; and transition metal.

In the light-emitting element having the above structure, the light isgenerated from the third layer 106 by applying the voltage between theanode 101 and the cathode 103 and by supplying the current of forwardbias in the electroluminescent layer 102. Thus, the light can beextracted from the side of the anode 101. It is noted that theelectroluminescent layer 102 does not always have to include all thesefirst to fifth layers. In the present invention, the electroluminescentlayer may include at least the light-emitting layer and one of theelectron-transporting layer and the electron-injecting layer. Inaddition, the light may be obtained not only from the third layer 106but also from another layer.

Depending on the color of the light, the phosphorescent material may beable to make the driving voltage lower and to provide higher reliabilitythan the fluorescent material. Consequently, when full-color display isperformed using the light-emitting element corresponding to each of thethree primary colors, the light-emitting element using the fluorescentmaterial and the light-emitting element using the phosphorescentmaterial may be combined so that the degree of deterioration is made thesame in the light-emitting elements of three primary colors.

Next, the structure of the light-emitting element in which the light canbe extracted from the cathode side is explained. FIG. 4B shows theLight-emitting element obtained by the present invention, which has ananode 111 formed over a substrate 110, an electroluminescent layer 112formed on the anode 111, and a cathode 113 formed on theelectroluminescent layer 112.

The anode 111 may be formed of a single layer including one or aplurality of elements selected from the group consisting of TiN, ZrN,Ti, W, Ni, Pt, Cr, Ag, and the like; two layers formed by laminating atitanium nitride film and a film mainly including aluminum; three layersformed by laminating a titanium nitride film, a film mainly includingaluminum, and a titanium nitride film; or the like. Moreover, the anode111 may be formed by laminating the conductive light-transmitting oxidelayer using ITO, indium tin oxide including silicon oxide (hereinafterreferred to as ITSO), IZO, or the like and the barrier layer on any oneof the above single layer, two layers, and three layers that can reflectthe light. In FIG. 4B, the anode 111 is formed by laminating an Al—Silayer 114, a Ti layer 115, a conductive light-transmitting oxide layer116, and a barrier layer 117 in order from the side of the substrate110.

The conductive light-transmitting oxide layer 116 is formed of theconductive light-transmitting oxide material and the silicon oxide. Thebarrier layer 117 is formed of the silicon oxide or formed of theconductive light-transmitting oxide material and the silicon oxide. Thedensity of the silicon is higher in the barrier layer 117 than in theconductive light-transmitting oxide layer 116.

The cathode 103 has light-transmitting property. Specifically, thecathode 103 may be formed of the conductive light-transmitting oxidematerial selected from the group consisting of the indium tin oxide(ITO), zinc oxide (ZnO), indium zinc oxide (IZO), gallium-doped zincoxide (GZO), and the like or may be formed of the silicon oxide and theconductive light-transmitting oxide material. In this case, it isdesirable that the electron-injecting layer is provided in theelectroluminescent layer so as to contact the cathode 103.

The cathode 103 may be formed of metal, alloy, conductive chemicalcompound, or mixture of these each of which has low work function andhas the thickness of such a degree that the light can transmit.Specifically, the cathode 103 can be formed of the alkali metal such asLi or Cs; alkali-earth metal such as Mg, Ca, or Sr; the alloy includingthese such as Mg:Ag or Al:Li; rare-earth metal such as Yb or Er in athickness from approximately 5 to 30 nm. In the case of providing theelectron-injecting layer, the cathode 103 can be formed of anotherconductive layer such as an Al film in the thickness of such a degreethat the light can transmit. In the case of forming the cathode 103 inthe thickness of such a degree that the light can transmit, theconductive light-transmitting oxide layer may be formed of theconductive light-transmitting oxide material on the cathode in order tosuppress the sheet resistance of the cathode.

The electroluminescent layer 112 may have the same structure as theelectroluminescent layer 102 shown in FIG. 4A. However, when the workfunction of the material used as the cathode is not low sufficiently, itis desirable to provide the electron-injecting layer.

Next, a method for manufacturing the light-emitting device of thepresent invention is explained in detail. The present embodiment modeexplains the example in which an n-channel TFT and a p-channel TFT aremanufactured over the same substrate.

As FIG. 5A indicates, a base film 202 is formed on a substrate 201. Asthe substrate 201, a glass substrate such as a bariumborosilicate glassor an aluminoborosilicate glass, a quartz substrate, a ceramicsubstrate, or the like can be used. In addition, a silicon substrate ora metal substrate including a stainless substrate with an insulatingfilm formed over the surface may be used. Although a substrate made offlexible synthetic resin such as plastic tends to be inferior to theabove substrates in point of the resistance against the heat, thesubstrate made of flexible synthetic resin can be used when it canresist the heat generated in the manufacturing process.

The base film 202 is provided in order to prevent alkaline-earth metalor alkali metal such as Na included in the substrate 201 from diffusinginto the semiconductor film and from causing an adverse effect on thecharacteristic of the semiconductor element such as a TFT. Therefore,the base film is formed of an insulating film such as silicon oxide,silicon nitride, or silicon nitride oxide, which can suppress thediffusion of the alkaline-earth metal and alkali metal into thesemiconductor film. In the present embodiment mode, a silicon nitrideoxide film is formed in a thickness from 10 to 400 nm (preferably from50 to 300 nm) by a plasma CVD method.

The base film 202 may be a single layer or a multilayer formed bylaminating a plurality of insulating films. In the case of using thesubstrate including the alkali metal or the alkaline-earth metal in anyway such as the glass substrate, the stainless substrate, or the plasticsubstrate, it is effective to provide the base film in terms ofpreventing the diffusion of the impurity. When the diffusion of theimpurity does not lead to any significant problems, for example when thequartz substrate is used, the base film does not always have to beprovided.

Next, island-shaped semiconductor films 203 and 204 used as an activelayer are formed on the base film 202 in a thickness from 25 to 100 nm(preferably from 30 to 60 nm). The island-shaped semiconductor films 203and 204 may be an amorphous semiconductor, a semi-amorphoussemiconductor (micro-crystal semiconductor), or a poly-crystallinesemiconductor. In addition, not only silicon but also silicon germaniumcan be used as the semiconductor. When the silicon germanium is used, itis preferable that the density of germanium is in the range of 0.01 to4.5 atomic %.

In the case of using the poly-crystalline semiconductor, an amorphoussemiconductor may be formed and then the amorphous semiconductor may becrystallized by a known crystallizing method. As the known crystallizingmethod, a crystallizing method by heating with the use of a heater, acrystallizing method by laser light irradiation, a crystallizing methodusing catalyst metal, or a crystallizing method using infrared light, orthe like is given.

When the crystallizing method by the laser light irradiation isemployed, a pulsed or continuous wave excimer laser, a YAG laser, a YVO₄laser, or the like may be used. For example, when the YAG laser is used,it is preferable to use a second harmonic, which is easily absorbed inthe semiconductor film. The pulsed repetition rate is set in the rangeof 30 to 300 kHz, the energy density is set in the range of 300 to 600mJ/cm² (typically in the range of 350 to 500 mJ/cm²), and the scanningspeed may be determined so that several shots can be irradiated to anypoint.

Next, a TFT is formed by using the island-shaped semiconductor films 203and 204. Although top-gate type TFTs 205 and 206 are formed using theisland-shaped semiconductor films 203 and 204 as shown in FIG. 5B inthis embodiment mode, the structure of the TFT is not limited to this,and the TFT may be a bottom-gate type.

Specifically, a gate insulating film 207 is formed so as to cover theisland-shaped semiconductor films 203 and 204. Then, a conductive filmis formed on the gate insulating film 207 and patterned, thereby forminggate electrodes 208 and 209. Subsequently, a source region, a drainregion, an LDD region, and the like are formed in such a way that animpurity imparting n-type or p-type is added to the island-shapedsemiconductor films 203 and 204 using the gate electrodes 208 and 209 asa mask or using the resist that is formed and patterned as a mask. It isnoted that the TFT 205 is n-type, and the TFT 206 is a p-type in thisembodiment mode.

It is noted that the gate insulating film 207 can be formed of siliconoxide, silicon nitride, silicon nitride oxide, or the like by a plasmaCVD method, a sputtering method, or the like. In the case of forming thegate insulating film using the silicon oxide by the plasma CVD method,the gate insulating film can be formed under the condition where themixed gas of TEOS (Tetraethyl Orthosilicate) and O₂ is used, thereaction pressure is 40 Pa, the substrate temperature ranges from 300 to400° C., and the electric density ranges from 0.5 to 0.8 W/cm² at highfrequency (13.56 MHz).

The gate insulating film 207 can be formed of aluminum nitride. The heatconductivity of the aluminum nitride is comparatively high and thereforethe heat generated in the TFT can be diffused efficiently. The gateinsulating film may be formed in such a way that after forming thesilicon oxide, silicon oxynitride, or the like not including aluminum,the aluminum nitride is formed thereon.

The above processes can form the n-channel TFT 205 and the p-channel TFT206 for controlling the current supplied to the light-emitting element.The manufacturing method of the TFT is not limited to the above. Thegate electrode and the wiring may be formed by a droplet dischargingmethod.

Next, a passivation film 210 is formed so as to cover the TFTs 205 and206. The passivation film 210 can be formed of the insulating filmincluding silicon such as silicon oxide, silicon nitride, or siliconoxynitride in a thickness from approximately 100 to 200 nm.

Next, a heat treatment is performed to activate the impurity elementadded in the island-shaped semiconductor films 203 and 204. Thistreatment can be performed by a thermal anneal method using an annealingfurnace, a laser anneal method, or a rapid thermal anneal (RTA) method.For example, when the thermal anneal method is used to activate theimpurity element, the heat treatment is performed under the atmosphereof nitrogen in which the density of oxygen is 1 ppm or less, preferably0.1 ppm or less, at temperatures ranging from 400 to 700° C. (preferablyfrom 500 to 600° C.). Moreover, another heat treatment is performedunder the atmosphere including hydrogen in the range of 3 to 100% attemperatures ranging from 300 to 450° C. for 1 to 12 hours tohydrogenate the island-shaped semiconductor film. This process is toterminate the dangling bond by the hydrogen excited thermally. Plasmahydrogenation (using hydrogen excited to be the plasma) may be performedas another means for hydrogenation. The activation process may beperformed before forming the passivation film 210.

Next, a first interlayer insulating film 211 and a second interlayerinsulating film 212 are formed to cover a passivation film 210 as shownin FIG. 5C. The first interlayer insulating film 211 can be formed of anorganic resin film, an inorganic insulating film, an insulating filmincluding Si—O bond and Si—CH_(x) bond made from the material selectedfrom the siloxane group, or the like. The insulating film formed usingthe material selected from the siloxane group is used in this embodimentmode. As the second interlayer insulating film 212, a film that is hardto transmit the material for promoting the deterioration of thelight-emitting element such as moisture or oxygen compared to anotherinsulating film is used. A silicon nitride film formed by an RFsputtering method is typically used. Moreover, a diamond-like-carbon(DLC) film, the aluminum nitride film, or the like can be also used.

Subsequently, the passivation film 210, the first interlayer insulatingfilm 211, and the second interlayer insulating film 212 are etched toform a contact hole. Then, wirings 213 to 216 to connect with theisland-shaped semiconductor films 203 and 204 are formed.

Next, a conductive light-transmitting oxide layer 217 is formed to coverthe second interlayer insulating film 212 and the wirings 213 to 216. Inthis embodiment mode, the conductive light-transmitting oxide layer 217is formed of the ITSO by the sputtering method. Not only the ITSO butalso indium oxide including silicon oxide with zinc oxide (ZnO) mixed inthe range of 2 to 20% may be used as the conductive light-transmittingoxide layer 217.

In the case of using the ITSO, the ITO including the silicon oxide inthe range of 2 to 10 wt. % can be used as the target. Specifically, theconductive light-transmitting oxide layer 217 is formed in 105 nm thickunder the condition where the target including In₂O₃ for 85 wt. %, SnO₂for 10 wt. %, and SiO₂ for 5 wt. % is used, the flow rate of Ar is 50sccm, the flow rate of O₂ is 3 sccm, the sputtering pressure is 0.4 Pa,the sputtering electric power is 1 kW, and the film-forming speed is 30nm/min.

In this embodiment mode, a barrier layer 218 having higher density of Sithan the conductive light-transmitting oxide layer 217 is formed on theconductive light-transmitting oxide layer 217. Specifically, the barrierlayer 218 is formed in 5 nm thick by the sputtering method using thetarget including In₂O₃ for 83 wt. %, SnO₂ for 7 wt. %, and SiO₂ for 10wt. %.

It is noted that the surface of the conductive light-transmitting oxidelayer 217 may be polished by a CMP method or by washing it using porousbody belonging to polyvinyl alcohol group before forming the barrierlayer 218 so that the surface of conductive light-transmitting oxidelayer 217 is flattened.

The barrier layer may be formed by removing the conductivelight-transmitting oxide material selectively from the surface ofconductive light-transmitting oxide layer and by increasing the densityof the added silicon. In this case, the barrier layer may be formedafter patterning the conductive light-transmitting oxide layer or afterforming a partition wall.

Next, as shown in FIG. 6A, an anode 219 connected to the wiring 216 isformed by patterning the conductive light-transmitting oxide layer 217and the barrier layer 218. A reference numeral 220 denotes the patternedconductive light-transmitting oxide layer and a reference numeral 221denotes the patterned barrier layer.

A partition wall 222 is formed on the second interlayer insulating film212. An organic resin film, an inorganic insulating film, an insulatingfilm including Si—O bond and Si—CH_(x) bond made from the materialselected from the siloxane group, or the like can be used as thepartition wall 222. The partition wall 222 is formed so as to cover theedge portion of the anode 219 and to have an opening in the regionoverlapping the anode 219. It is preferable to make the edge portion ofthe opening of the barrier 222 round so as to prevent theelectroluminescent layer to be formed afterward from boring. Morespecifically, it is desirable that the sectional surface of the barrier222 at the edge of the opening has a radius of curvature ranging fromapproximately 0.2 to 2 μm.

FIG. 6A shows an example using positive photosensitive acrylic resin asthe barrier 222. In the photosensitive organic resin, there are thepositive type in which the region where the energy such as light,electron, ion, or the like is exposed is removed and the negative typein which the region that is exposed is not removed. The presentinvention may use the negative organic resin. Moreover, a photosensitivepolyimide may be used to form the barrier 222. In the case of formingthe barrier 222 using the negative acrylic, the edge portion of theopening shapes like a letter of S. On this occasion, it is desirablethat the radius of curvature in the upper portion and the lower portionof the opening is in the range of 0.2 to 2 μm.

With the above structure, the coverage of the electroluminescent layerand the cathode to be formed afterward can be improved and it ispossible to prevent the electroluminescent layer from boring. As aresult, the anode 219 and the cathode are prevented from shorting.Moreover, when the stress of the electroluminescent layer is relaxed, itis possible to decrease the defect called shrink in which thelight-emitting region decreases and to enhance the reliability.

Next, a heat treatment is performed under the atmosphere or a heattreatment (vacuum bake) is performed under the vacuum atmosphere beforeforming the electroluminescent layer in order to remove the moisture,oxygen, and the like adsorbed on the barrier 222 and the anode 219.Specifically, the heat treatment is performed under the vacuumatmosphere at the temperature of the substrate ranging from 200 to 450°C., preferably from 250 to 300° C., for approximately 0.5 to 20 hours.It is desirable that the pressure is set to 3×10⁻⁷ Torr or less, and itis the most desirable that the pressure is set to 3×10⁻⁸ Torr or less ifpossible. When the electroluminescent layer is formed after the heattreatment under the vacuum atmosphere, the reliability can be furtherenhanced by keeping the substrate under the vacuum atmosphere until justbefore forming the electroluminescent layer. The anode 219 may beirradiated with an ultraviolet ray before or after the vacuum bake.

Next, as shown in FIG. 6B, an electroluminescent layer 223 is formed onthe anode 219. The electroluminescent layer 223 includes one or aplurality of layers and each layer may include not only an organicmaterial but also an inorganic material. The above explanation aboutFIGS. 4A and 4B can be referred to for the detail of the structure ofthe electroluminescent layer 223. Subsequently, the cathode 224 isformed so as to cover the electroluminescent layer 223. The anode 219,the electroluminescent layer 223, and the cathode 224 overlap in theopening of the barrier 222. The region in which these overlapcorresponds to a light-emitting element 225.

After forming the light-emitting element 225, a protective film may beformed on the cathode 224. The film that is hard to transmit thematerial to promote the deterioration of the light-emitting element suchas moisture or oxygen compared to another insulating film is used as theprotective film as well as the second interlayer insulating film 212.Typically, it is desirable to use the DLC film, a carbon nitride film, asilicon nitride film formed by the RF sputtering method, or the like.Moreover, the above-mentioned film, which is hard to transmit themoisture or oxygen, and a film that transmits the moisture or oxygenmore easily than the above film can be laminated and used as theprotective film.

Although FIG. 6B shows the structure in which the light emitted from thelight-emitting element is irradiated to the side of the substrate 201,the light-emitting element may have the structure in which the light isemitted to the side opposite to the substrate.

It is noted that after the light-emitting device shown in FIG. 6B isobtained, it is preferable to package (enclose) the light-emittingdevice using a protective film (laminated film, ultraviolet curableresin film, or the like) or a light-transmitting cover member that ishighly airtight and hardly degasses. The reliability of thelight-emitting element is enhanced when the inside of the cover memberis filled with the inert atmosphere or the material havingmoisture-absorption characteristic (barium oxide, for example) is set inthe cover member.

The method for manufacturing a light-emitting device of the presentinvention is not limited to that shown above. This embodiment modeexplains just one example of the manufacturing method of the presentinvention, and various changes can be made within the scope of thepresent invention.

Embodiment 1

The present embodiment explains an example of a pixel of thelight-emitting device obtained by the manufacturing method of thepresent invention.

FIG. 8 is a cross-sectional view of the light-emitting device explainedin the present embodiment. In FIG. 8, transistors 7001 to 7003 areformed over a substrate 7000. The transistors 7001 to 7003 are coveredby a first interlayer insulating film 7004. Wirings 7005 to 7007connecting with the transistors 7001 to 7003 through the contact holeare formed on the first interlayer insulating film 7004.

A second interlayer insulating film 7008 and a third interlayerinsulating film 7009 are laminated over the first interlayer insulatingfilm 7004 so as to cover the wirings 7005 to 7007. It is noted that theorganic resin film, the inorganic insulating film, the insulating filmincluding Si—O bond and Si—CH_(x) bond made from the material selectedfrom the siloxane group, or the like can be used as the material of thefirst interlayer insulating film 7004 and the second interlayerinsulating film 7008. In this embodiment, a non-photosensitive acrylicis used. A film that is hard to transmit the material to promote thedeterioration of the light-emitting element such as moisture or oxygencompared to another insulating film is used as the material of the thirdinterlayer insulating film 7009. Typically, it is desirable to use theDLC film, the carbon nitride film, the silicon nitride film formed bythe RF sputtering method, or the like.

Wirings 7010 to 7012 connected electrically with the wirings 7005 to7007 through the contact hole are formed on the third interlayerinsulating film 7009. The wirings 7010 to 7012 are formed of thematerial through which the light does not transmit. Conductivelight-transmitting oxide layers 7013 to 7015 and barrier layers 7016 to7018 are laminated over the wirings 7010 to 7012. A part of the wirings7010 to 7012, the conductive light-transmitting oxide layers 7013 to7015, and the barrier layers 7016 to 7018 form anodes 7019 to 7021.

In FIG. 8, since the anodes 7019 to 7021 and the wirings 7010 to 7012connected directly to the TFT are formed in the different layer, it ispossible to enlarge the square measure of the layout of the anodes 7019to 7021 and therefore to enlarge the region of the light-emittingelement from which the light is obtained.

Moreover, a barrier 7040 is formed using an insulating film includingSi—O bond and Si—CH_(x) bond made from the material selected from thesiloxane group, the organic resin film, the inorganic insulating film,or the like on the third interlayer insulating film 7009. The barrier7040 has an opening, and light-emitting elements 7026 to 7028 are formedby overlapping the anodes 7019 to 7021, the electroluminescent layers7022 to 7024, and the cathode 7025 in the opening The electroluminescentlayers 7022 to 7024 have a structure in which a plurality of layers islaminated. The cathode 7025 is formed of the material through which thelight can transmit or in the thickness of such a degree that the lighttransmits. A protective film may be formed over the barrier 7040 and thecathode 7025.

A reference numeral 7030 denotes a light-transmitting cover member forsealing the light-emitting elements 7026 to 7028. A color filter 7035having a blocking film 7031 for blocking the visible light and havingcoloring layers 7032 to 7034 corresponding to the pixel of each color isformed on the cover member 7030. In FIG. 8, the light in the redwavelength region among the light emitted from the light-emittingelement 7026 transmits through the coloring layer 7032 selectively. Thelight in the green wavelength region among the light emitted from thelight-emitting element 7027 transmits through the coloring layer 7033selectively. The light in the blue wavelength region among the lightemitted from the light-emitting element 7028 transmits through thecoloring layer 7034 selectively.

In FIG. 8, the blocking film 7031 is formed in such a way that blackpigment and drying agent are diffused in the resin. With the abovestructure, the deterioration of the light-emitting element can beprevented.

The blocking film 7031 is provided between the light-emitting elements7026 and 7027 and between the light-emitting elements 7027 and 7028. Theblocking film 7031 prevents the light generated in the light-emittingelement from transmitting through the coloring layer of the adjacentpixels.

Although FIG. 8 explains the electroluminescent layers 7022 to 7024 eachof which includes different electroluminescent material or has differentelement structure in every pixel corresponding to each color, thepresent invention is not limited to this. The electroluminescent layerseach of which includes different electroluminescent material or hasdifferent element structure at least in the pixels corresponding to twocolors may be used.

The color filter can enhance colorimetric purity of the light extractedfrom the pixel even though the colorimetric purity of the light emittedfrom each light-emitting element is low to some extent. It is desirablethat the spectrum of the light emitted from the light-emitting elementhas comparatively higher peak in the wavelength region of thecorresponding color than in the other wavelength regions. For example,in the case of the pixel of the red color, it is preferable that thespectrum of the light emitted from the light-emitting element hascomparatively high peak in the red wavelength region. With the abovestructure, the amount of blocked light can be suppressed in every pixelof each color. Therefore, the light can be extracted efficientlycompared to the case using the light-emitting element of white color.

The airtight space formed between the cover member 7030 and thesubstrate 7000 is filled with the inert gas or resin, or the materialhaving moisture-absorption characteristic (such as barium oxide) may beset in the space.

Although the color filter is provided on the cover member in FIG. 8, thepresent invention is not limited to this structure. For example, thecoloring layer maybe formed so as to overlap the light-emitting elementby a droplet discharging method or the like. In this case, the resin canbe used instead of the cover member. When the resin is used to seal thelight-emitting element, the light extraction efficiency can be enhancedcompared to the case where the cover member is provided.

It is noted that the light-emitting device of the present invention canbe manufactured not only by the above manufacturing method but also by aknown method.

Embodiment 2

This embodiment explains a circuit diagram of a pixel of alight-emitting device manufactured by the present invention withreference to FIGS. 9A to 9C. FIG. 9A is an equivalent circuit diagram ofthe pixel showing a signal line 6114, power supply lines 6115 and 6117,a scanning line 6116, a light-emitting element 6113, a TFT 6110 forcontrolling the input of a video signal into the pixel, a TFT 6111 forcontrolling the current value flowing between both electrodes of thelight-emitting element 6113, and a capacitance element 6112 for holdingthe voltage between the gate and the source of the TFT 6111. AlthoughFIG. 5B shows the capacitance element 6112, the capacitance element 6112is not necessary when the gate capacitance of the TFT 6111 or anotherparasitic capacitance is enough.

FIG. 9B is a pixel circuit having the structure in which a TFT 6118 anda scanning line 6119 are newly provided in the pixel shown in FIG. 9A.The TFT 6118 makes it possible to make the condition compellingly inwhich the current does not flow in the light-emitting element 6113.Thus, the lighting period can start at the same time as or just afterthe start of the writing period without waiting the writing of thesignal to all the pixels. Therefore, the duty ratio increases andparticularly the display of the moving image can be improved.

FIG. 9C is a pixel circuit in which a TFT 6125 and a wiring 6126 areprovided in the pixel shown in FIG. 9B. In this structure, a gateelectrode of the TFT 6125 is connected to the wiring 6126 with thepotential kept constant so that the potential of this gate electrode isfixed and that the TFT 6125 is operated in a saturated region. A videosignal for conveying the information of lightening or not lightening ofthe pixel is input through the TFT 6110 into a gate electrode of the TFT6111 that is connected to the TFT 6125 serially and that operates in alinear region. Since the voltage value between the source and the drainof the TFT 6111 operating in the linear region is low, the slightfluctuation of the voltage between the source and the drain of the TFT6111 does not affect the current value flowing in the light-emittingelement 6113. Therefore, the current value flowing in the light-emittingelement 6113 is determined by the TFT 6125 operating in the saturatedregion. In the present invention having the above structure, the imagequality can be enhanced by improving the inhomogeneous luminance of thelight-emitting element 6113 due to the variation in the characteristicof the TFT 6125. It is preferable that L₁/W₁:L₂/W₂=5 to 6000: 1 issatisfied when the channel length of the TFT 6125 is L₁, the channelwidth thereof is W₁, the channel length of TFT 6111 is L₂, and thechannel width thereof is W₂. Moreover, it is preferable that both TFTshave the same conductivity type in the manufacturing step. As the TFT6125, not only an enhancement type but also a depletion type may beused.

One of an analog video signal and a digital video signal may be used inthe light-emitting device formed by the present invention. In thedigital video signal, there are a video signal using the voltage and avideo signal using the current. In other words, the video signal inputinto the pixel uses the constant voltage or the constant current whenthe light-emitting element emits light. When the video signal uses theconstant voltage, the voltage applied to the light-emitting element orthe current flowing in the light-emitting element is constant. On theother hand, when the video signal uses the constant current, the voltageapplied to the light-emitting element or the current flowing in thelight-emitting element is constant. The former one in which the constantvoltage is applied to the light-emitting element is referred to as aconstant voltage drive, while the latter one in which the constantcurrent flows in the light-emitting element is referred to as a constantcurrent drive. The constant current flows in the light-emitting elementdriven by the constant current without being affected by the change ofthe resistance of the light-emitting element. Either the video signalusing the constant voltage or the video signal using the constantcurrent may be used in the light-emitting device and its driving method.Moreover, the light-emitting device of the present invention may be usedeither by the constant voltage drive or by the constant current drive.The present embodiment can be freely combined with the embodiment modeand another embodiment.

Embodiment 3

The present embodiment explains a structure of a light-emitting devicemanufactured by the present invention with reference to FIGS. 10A to10F. FIG. 10A is a top view of the light-emitting device for explainingthe concept of the light-emitting device having a pixel portion 6201, asignal line driver circuit 6202, and a scanning line driver circuit 6203over a substrate 6200. A reference numeral 6204 denotes an inputterminal for supplying power source potential or a signal to eachcircuit formed over the substrate 6200. Reference numerals 6205 to 6207denote protective circuits for preventing the semiconductor element frombeing damaged due to the noise of the signal, the electrostatic, or thelike. It is not always necessary to provide all the protective circuits6205 to 6207 and any one or a plurality of protective circuits amongthem may be provided.

Although the signal line driver circuit 6202 and the scanning linedriver circuit 6203 are formed over the substrate 6200 where the pixelportion 6201 is formed, the present invention is not limited to thisstructure. For example, when an amorphous semiconductor or amicro-crystal semiconductor is used as a semiconductor element forforming the pixel portion 6201, the signal line driver circuit 6202 andthe scanning line driver circuit 6203 formed separately may be mountedon the substrate 6200 by a known method such as a COG method or a TABmethod. When the micro-crystal semiconductor is used as thesemiconductor element for forming the pixel portion 6201, the scanningline driver circuit and the pixel portion may be formed of themicro-crystal semiconductor over the same substrate, and the signal linedriver circuit may be mounted on this substrate. Moreover, a part of thescanning line driver circuit or a part of the signal line driver circuitis formed together with the pixel portion over the same substrate andthen the other parts of the scanning line driver circuit or the otherparts of the signal line driver circuit may be mounted on thissubstrate. In other words, there are various ways to form the drivingcircuit and any structure can be used in the present invention.

Next, an example of the protective circuits 6205 to 6207 used in thelight-emitting device manufactured by the present invention isexplained. The protective circuit is formed by one or a plurality ofsemiconductor elements selected from the group consisting of a TFT, adiode, a resistance element, a capacitance element, and the like.Hereinafter structures of several protective circuits and theiroperations are explained.

First, a structure of the protective circuit 6205 provided between theinput terminal and each circuit formed over the substrate is explainedwith reference to an equivalent circuit diagram in FIG. 10B. Theprotective circuit shown in FIG. 10B has p-channel TFTs 7220 and 7230,capacitance elements 7210 and 7240, and a resistance element 7250. Theresistance element 7250 has two terminals. The input potential Vin givenfrom the input terminal is given to one terminal and the low powersource potential VSS is given to the other terminal. The resistanceelement 7250 is provided in order to lower the potential of the wiringto be VSS when the Vin is not given to the input terminal, and theresistance value of the resistance element 7250 is set so as to becomemuch higher than that of the wiring.

According to the relation of the voltage between the gate and thesource, the TFT 7220 is turned on and the TFT 7230 is turned off whenVin is higher than the high power source potential VDD. Then, VDD isgiven to the wiring through the TFT 7220. Therefore, even though Vinbecomes higher than VDD due to the noise or the like, the potentialgiven to the wiring does not become higher than VDD. On the other hand,according to the relation of the voltage between the gate and thesource, the TFT 7220 is turned off and the TFT 7230 is turned on whenVin is lower than VSS. Then, VSS is given to the wiring. Therefore, eventhough Vin becomes lower than VSS due to the noise or the like, thepotential given to the wiring does not become lower than VSS. Moreover,a pulsed noise can be reduced in the potential from the input terminalby the capacitance elements 7210 and 7240 and it is possible to suppressthe sudden change of the potential due to the noise to some extent.

With the arrangement of the protective circuits in the above structure,the potential of the wiring is kept between VSS and VDD, and the circuitin the following line can be protected from the extremely high orextremely low potential out of this range. Moreover, by providing theprotective circuit in the input terminal where the signal is input, thepotential of all the wirings to which the signal is given can be keptconstant (VSS here) when the signal is not input. In other words, theprotective circuit has a function as a short ring to make the wiringsshorted when the signal is not input. Therefore, the electrostaticdamage due to the potential difference between the wirings can beprevented. Moreover, since the resistance value of the resistanceelement 7250 is high sufficiently when the signal is input, the signalgiven to the wiring is not affected by VSS.

FIG. 10C is an equivalent circuit diagram of the protective circuit inwhich rectifier diodes 7260 and 7270 are used instead of the p-channelTFTs 7220 and 7230. FIG. 10D is an equivalent circuit diagram of theprotective circuit in which TFTs 7350, 7360, 7370, and 7380 are usedinstead of the p-channel TFTs 7220 and 7230.

As a protective circuit having the structure different from thatdescribed above, protective circuits shown in FIGS. 10E and 10F aregiven. The protective circuit shown in FIG. 10E has resistances 7280,7290, and an n-channel TFT 7300. The protective circuit shown in FIG.10F has resistances 7280 and 7290, a p-channel TFT 7310, and ann-channel 111 7320. In both structures of FIGS. 10E and 10F, the wiringand the like are connected to the terminal 7330, and the current flowsin a direction from the terminal 7330 to the terminal 7340 by turning onthe n-channel TFT 7300 or by turning on the p-channel TFT 7310 and then-channel TFT 7320 when the potential of this wiring and the likechanges suddenly. Thus, it is possible to relax the sudden change of thepotential connected to the terminal 7330 and to prevent thesemiconductor element from deteriorating or being damaged. It ispreferable that the semiconductor element of the protective circuit isformed of an amorphous semiconductor that is superior in resistance. Thepresent embodiment can be freely combined with the above embodimentmode.

It is noted that the signal line driver circuit 6202 and the pixelportion 6201 are connected by the signal line and the protective circuit6206 can prevent the potential of the signal line from changing suddenlydue to the noise or the electrostatic. The scanning line driver circuit6203 and the pixel portion 6201 are connected by the scanning line, andthe protective circuit 6207 can prevent the potential of the scanningline from changing suddenly due to the noise or the electrostatic. Theprotective circuits 6206 and 6207 can have the circuit structure shownin any one of FIGS. 10B to 10F as well as the protective circuit 6205.

Embodiment 4

This embodiment explains a panel, which is an example of alight-emitting device manufactured by the present invention, withreference to FIGS. 11A and 11B. FIG. 11A is a top view of the panel inwhich the transistor and the light-emitting element formed over thesubstrate are sealed between the substrate and the cover member by asealing material. FIG. 11B is a side view taken along A-A′ in FIG. 11A.

A sealing material 4005 is provided so as to surround a pixel portion4002, a signal line driver circuit 4003, and a scanning line drivercircuit 4004 all of which are formed over the substrate 4001. Moreover,a cover member 4006 is provided over the pixel portion 4002, the signalline driver circuit 4003, and the scanning line driver circuit 4004.Therefore, the pixel portion 4002, the signal line driver circuit 4003,and the scanning line driver circuit 4004 are sealed with a fillermaterial 4007 by the substrate 4001, the sealing material 4005, and thecover member 4006.

The pixel portion 4002, the signal line driver circuit 4003, and thescanning line driver circuit 4004 all of which are formed over thesubstrate 4001 have a plurality of transistors, and FIG. 11B showstransistors 4008 and 4009 in the signal line driver circuit 4003 and atransistor 4010 in the pixel portion 4002.

A reference numeral 4011 denotes a light-emitting element, which isconnected electrically to the transistor 4010.

The lead wiring 4014 is a wiring for supplying a signal or power supplyvoltage to the pixel portion 4002, the signal line driver circuit 4003,and the scanning line driver circuit 4004. The lead wiring 4014 isconnected to a connection terminal 4016 through the lead wiring 4015.The connection terminal 4016 is connected electrically to the terminalin an FPC 4018 through an anisotropic conductive film 4019.

As the substrate 4001, not only glass, metal (typically stainless), andceramic but also flexible material typified by plastic can be used. Asthe plastic, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF(polyvinylfluoride) film, a mylar film, a polyester film, or an acrylicresin film can be used. Moreover, a sheet in which an aluminum foil issandwiched by the PVF film or the mylar film can be used. The covermember 4006 is formed of the light-transmitting material such as a glassplate, a plastic plate, a polyester film, or an acrylic film.

As the filler material 4007, not only inert gas such as nitrogen orargon but also ultraviolet curable resin or thermoset resin can be used.For example, PVC (polyvinylchloride), acrylic, polyimide, epoxy resin,silicon resin, PVB (polyvinylbutyral), or EVA (ethylene vinyl acetate)can be used. Nitrogen is used as the filler material in this embodiment.

The filler material 4007 may be exposed to the material having themoisture-absorption characteristic (preferably barium oxide) or thematerial that can absorb the oxygen.

Embodiment 5

In the light-emitting device of the present invention, the externalquantum efficiency is high in spite of the low power consumption and thecontrast of the image can be enhanced. Therefore, even when the outsidelight such as sunlight is irradiated, the clear image can be displayedwhile suppressing the power consumption, and therefore thelight-emitting device of the present invention has an advantageouseffect that it can be used in any place. For this reason, the presentinvention is suitable not only for the television but also for a mobileelectronic equipment.

Specifically, as the electronic equipment using the light-emittingdevice of the present invention, there are a video camera, a digitalcamera, a goggle type display (head mount display), a navigation system,a sound reproduction device (car audio, an audio compo, and the like), anote type personal computer, a game machine, a mobile terminal device(mobile computer, mobile phone, mobile game machine, an electronic book,or the like), an image reproduction device with a recording mediumequipped (specifically, a device for playing a recording medium such asDVD (Digital Versatile Disc) and for displaying the image), and thelike. FIGS. 12A to 12C show the examples of these electronic equipments.

FIG. 12A is a display device including a chassis 2001, a supportingstand 2002, a display portion 2003, a speaker portion 2004, a videoinput terminal 2005, and the like. The light-emitting device of thepresent invention can be used as the display portion 2003. Since thelight-emitting device emits the light by itself, the backlight is notnecessary and therefore the display portion can be made thinner than aliquid crystal display. The display device using the light-emittingelement includes all the display devices for displaying information suchas the display device for a personal computer, for TV broadcastreceiving, or for displaying an advertisement.

FIG. 12B is a note-type personal computer including a main body 2201, achassis 2202, a display portion 2203, a keyboard 2204, an externalconnection port 2205, a mouse 2206, and the like. The light-emittingdevice of the present invention can be used as the display portion 2203.

FIG. 12C is a personal digital assistant (PDA) including a main body2101, a display portion 2102, an operation key 2103, a modem 2104, andthe like. The modem 2104 may be incorporated in the main body 2101. Thelight-emitting device of the present invention can be used as thedisplay portion 2102.

As above, the present invention can be applied in a wide range and canbe applied to various kinds of electronic equipments. In addition, theelectronic equipments of this embodiment may have the light-emittingdevice having any structure shown in the embodiments 1 to 4.

Embodiment 6

A transistor used in the light-emitting device of the present inventionmay be a TFT using a poly-crystalline semiconductor or may be a TFTusing an amorphous semiconductor or a semi-amorphous semiconductor. Thisembodiment explains a structure of the TFT formed using the amorphoussemiconductor or the semi-amorphous semiconductor.

FIG. 7A is a cross-sectional view of the TFT used in a driving circuitand a cross-sectional view of the TFT used in a pixel portion. Areference numeral 1001 denotes a cross section of the TFT used in thedriving circuit, a reference numeral 1002 denotes a cross section of theTFT used in the pixel portion, and a reference numeral 1003 denotes across section of a light-emitting element to which the current issupplied by the TFT 1002. The TFTs 1001 and 1002 are inversely staggered(bottom-gate type) TFTs.

The TFT 1001 in the driving circuit includes a gate electrode 1010 overa substrate 1000, a gate insulating film 1011 covering the gateelectrode 1010, and a first semiconductor film 1012 formed of thesemi-amorphous semiconductor or the amorphous semiconductor thatoverlaps the gate electrode 1010 with the gate insulating film 1011interposed therebetween. Moreover, the TFT 1001 has a pair of secondsemiconductor films 1013 functioning as a source region or a drainregion and a third semiconductor film 1014 provided between the firstsemiconductor film 1012 and the second semiconductor film 1013.

Although the gate insulating film 1011 is formed of two layers ofinsulating film in FIG. 7A, the present invention is not limited to thisstructure. The gate insulating film 1011 may be formed of a single layeror three or more layers of the insulating film.

The second semiconductor film 1013 is formed of the amorphoussemiconductor or the semi-amorphous semiconductor, and an impurityimparting one conductivity type is added to the second semiconductorfilm 1013. The pair of second semiconductor films 1013 is providedoppositely with a region in the first semiconductor film 1012 where achannel is formed interposed therebetween.

The third semiconductor film 1014 is formed of the amorphoussemiconductor or the semi-amorphous semiconductor. The thirdsemiconductor film 1014 has the same conductivity type as the secondsemiconductor film 1013 and has the characteristic that the conductivitythereof is lower than that of the second semiconductor film 1013. Sincethe third semiconductor film 1014 works as the LDD region, the electricfield concentrated in the end portion of the second semiconductor film1013 functioning as the drain region can be relaxed and the hot carriereffect can be prevented. Although the third semiconductor film 1014 isnot always necessary, the provision of the third semiconductor film 1014can improve the withstand voltage of the TFT and can enhance thereliability. When the TFT 1001 is n-type, the third semiconductor film1014 can have n-type conductivity without adding the impurity impartingn-type in particular when forming the third semiconductor film 1014.Therefore, when the TFT 1001 is n-type, the impurity imparting n-typedoes not always have to be added to the third semiconductor film 1014.However, an impurity imparting p-type conductivity is added to the firstsemiconductor film where the channel is formed and the conductivity typeis controlled so as to approach I-type as much as possible.

Two wirings 1015 are formed so as to contact the pair of secondsemiconductor films 1013.

The TFT 1002 in the driving circuit includes a gate electrode 1020 overthe substrate 1000, a gate insulating film 1011 covering the gateelectrode 1020, and a first semiconductor film 1022 formed of theamorphous semiconductor or the semi-amorphous semiconductor thatoverlaps the gate electrode 1020 with the gate insulating film 1011interposed therebetween. Moreover, the TFT 1002 has a pair of secondsemiconductor films 1023 functioning as a source region or a drainregion and a third semiconductor film 1024 provided between the firstsemiconductor film 1022 and the second semiconductor film 1023.

The second semiconductor film 1023 is formed of the amorphoussemiconductor or the semi-amorphous semiconductor, and the impurityimparting one conductivity type is added to the second semiconductorfilm 1023. The pair of second semiconductor films 1023 is providedoppositely with a region in the first semiconductor film 1022 where thechannel is formed interposed therebetween.

The third semiconductor film 1024 is formed of the amorphoussemiconductor or the semi-amorphous semiconductor. The thirdsemiconductor film 1024 has the same conductivity type as the secondsemiconductor film 1023 and has the characteristic that the conductivitythereof is lower than that of the second semiconductor film 1023. Sincethe third semiconductor film 1024 works as the LDD region, the electricfield concentrated in the end portion of the second semiconductor film1023 functioning as the drain region can be relaxed and the hot carriereffect can be prevented. Although the third semiconductor film 1024 isnot always necessary, the provision of the third semiconductor film 1024can improve the withstand voltage of the TFT and can enhance thereliability. When the TFT 1002 is n-type, the third semiconductor film1024 can have n-type conductivity without adding the impurity impartingn-type in particular when forming the third semiconductor film 1024.Therefore, when the TFT 1002 is n-type, the impurity imparting n-typedoes not always have to be added to the third semiconductor film 1024.However, an impurity imparting p-type conductivity is added to the firstsemiconductor film where the channel is formed, and the conductivitytype is controlled so as to approach I-type as much as possible.

Moreover, a wiring 1025 is formed so as to contact the pair of secondsemiconductor films 1023.

In addition, a first passivation film 1040 and a second passivation Elm1041 are formed of the insulating film so as to cover the TFTs 1001 and1002 and the wirings 1015 and 1025. The passivation film covering theTFTs 1001 and 1002 may have not only two layers but also a single layeror three or more layers. For example, the first passivation film 1040can be formed of silicon nitride and the second passivation film 1041can be formed of silicon oxide. When the passivation film is formed ofthe silicon nitride or the silicon nitride oxide, it is possible toprevent the TFTs 1001 and 1002 from deteriorating due to the moisture oroxygen.

One of the wirings 1025 is connected to the anode 1030 of thelight-emitting element 1003. Moreover, an electroluminescent layer 1031is formed so as to contact on the anode 1030 and a cathode 1032 isformed so as to contact on the electroluminescent layer 1031.

The anode 1030 has a conductive light-transmitting oxide layer 1030 aand a barrier layer 1030 b, and the barrier 1030 b contacts theelectroluminescent layer 1031.

Next, another example of a TFT in the light-emitting device of thepresent invention that is different from the TFT shown in FIG. 7A isexplained. FIG. 7B is a cross-sectional view of the TFT used in thedriving circuit and a cross-sectional view of a TFT used in the pixelportion. A reference numeral 1101 denotes a cross section of the TFTused in the driving circuit, a reference numeral 1102 denotes a crosssection of the TFT used in the pixel portion, and a reference numeral1103 denotes a cross section of a light-emitting element to which thecurrent is supplied by the TFT 1102.

The TFT 1101 in the driving circuit and the TFT 1102 in the pixelportion respectively include gate electrodes 1110 and 1120 over asubstrate 1100, a gate insulating film 1111 covering the gate electrodes1110 and 1120, and first semiconductor films 1112 and 1122 formed of theamorphous, semiconductor or the semi-amorphous semiconductor thatoverlap the gate electrodes 1110 and 1120 with the gate insulating film1111 interposed therebetween. Channel protective films 1133 and 1134 areformed of the insulating film so as to cover the channel-forming regionof the first semiconductor films 1112 and 1122. The channel protectivefilms 1133 and 1134 are provided in order to prevent the channel-formingregions of the first semiconductor films 1112 and 1122 from being etchedin the process for manufacturing the TFTs 1101 and 1102. Moreover, theTFT 1101 has a pair of second semiconductor films 1113 and has a thirdsemiconductor film 1114 provided between the first semiconductor film1112 and the second semiconductor film 1113. The TFT 1102 has a pair ofsecond semiconductor films 1123 and has a third semiconductor film 1124provided between the first semiconductor film 1122 and the secondsemiconductor film 1123.

Although the gate insulating film 1111 is formed of two layers ofinsulating film in FIG. 7B, the present invention is not limited to thisstructure. The gate insulating film 1111 may be formed of a single layeror three or more layers of the insulating film.

The second semiconductor films 1113 and 1123 are formed of the amorphoussemiconductor or the semi-amorphous semiconductor, and an impurityimparting one conductivity type is added to the second semiconductorfilms 1113 and 1123. The respective pairs of second semiconductor films1113 and 1123 are formed oppositely with a region in the firstsemiconductor films 1112 and 1122 where a channel is formed interposedtherebetween.

The third semiconductor films 1114 and 1124 are formed of the amorphoussemiconductor or the semi-amorphous semiconductor. The thirdsemiconductor films 1114 and 1124 have the same conductivity type as thesecond semiconductor films 1113 and 1123 and have the characteristicthat the conductivity thereof is lower than that of the secondsemiconductor films 1113 and 1123. Since the third semiconductor films1114 and 1124 work as the LDD region, the electric field concentrated inthe end portion of the second semiconductor films 1113 and 1123functioning as the drain region can be relaxed and the hot carriereffect can be prevented. Although the third semiconductor films 1114 and1124 are not always necessary, the provision of the third semiconductorfilms 1114 and 1124 can improve the withstand voltage of the TFT and canenhance the reliability. When the TFTs 1101 and 1102 are n-type, thethird semiconductor films 1114 and 1124 can have n-type conductivitywithout adding the impurity imparting n-type when forming the thirdsemiconductor films 1114 and 1124. Therefore, when the TFTs 1101 and1102 are n-type, the impurity imparting n-type does not always have tobe added to the third semiconductor films 1114 and 1124. However, animpurity imparting p-type conductivity is added to the firstsemiconductor film where the channel is formed and the conductivity typeis controlled so as to approach I-type as much as possible.

Two wirings 1115 are formed so as to contact the pair of secondsemiconductor films 1113, and two wirings 1125 are formed to contact thepair of second semiconductor films 1123.

A first passivation film 1140 is formed of the insulating film so as tocover the TFT 1101 and the wiring 1115. A second passivation film 1141is formed of the insulating film so as to cover the TFT 1102 and thewiring 1125. The passivation films covering the TFTs 1101 and 1102 mayhave not only two layers but also a single layer or three or morelayers. For example, the first passivation film 1140 can be formed ofsilicon nitride and the second passivation film 1141 can be formed ofsilicon oxide. When the passivation film is formed of the siliconnitride or the silicon nitride oxide, it is possible to prevent the TFTs1101 and 1102 from deteriorating due to the moisture or oxygen.

One of the wirings 1125 is connected to the anode 1130 of thelight-emitting element 1103. Moreover, an electroluminescent layer 1131is formed so as to contact on the anode 1130 and a cathode 1132 isformed so as to contact the electroluminescent layer 1131.

The anode 1130 has a conductive light-transmitting oxide layer 1130 aand a barrier layer 1130 b, and the barrier layer 1130 b contacts theelectroluminescent layer 1134.

Although this embodiment explains an example where the driving circuitand the pixel portion of the light-emitting device are formed over thesame substrate using the TFT formed by the amorphous semiconductor orthe semi-amorphous semiconductor, the present invention is not limitedto this. The pixel portion may be formed over a substrate by the TFTusing the amorphous semiconductor or the semi-amorphous semiconductorand a driving circuit formed separately may be pasted to the substratewith the pixel portion formed.

Moreover, the gate electrode and the wiring may be formed by the dropletdischarging method. FIG. 13A shows a cross section of the pixel formedby the droplet discharging method as an example. In FIG. 13A, areference numeral 1201 denotes a bottom-gate TFT, which is connectedelectrically to the light-emitting element 1202. The TFT 1201 has a gateelectrode 1203, a gate insulating film 1204 formed on the gate electrode1203, a first semiconductor film 1205 formed on the gate insulating film1204, and a second semiconductor film 1206 formed on the firstsemiconductor film 1205. It is noted that the first semiconductor film1205 functions as the channel-forming region. An impurity impartingconductivity type is added to the second semiconductor film 1206, whichfunctions as a source region or a drain region.

The wiring 1208 is formed so as to contact the second semiconductor film1206, and the wiring 1208 is connected to the anode 1209 in thelight-emitting element 1202. In addition, the light-emitting element1202 has an anode 1209, an electroluminescent layer 1210 formed on theanode 1209, and a cathode 1211 formed on the electroluminescent layer1210. The anode 1209 has a conductive light-transmitting oxide layer1209 a and the barrier layer 1209 b.

In the light-emitting device shown in FIG. 13A, the gate electrode 1203,the wiring 1208, the anode 1209, the electroluminescent layer 1210, amask used for patterning, and the like can be formed by the dropletdischarging method.

FIG. 13B shows a cross section of the pixel formed by the dropletdischarging method as an example. In FIG. 13B, an insulating film(etching stopper) 1224 is formed on the first semiconductor film 1221 ofthe bottom-gate type TFT 1220 for the purpose of preventing the firstsemiconductor film 1221 from being etched when patterning the secondsemiconductor film 1222 and the wiring 1223.

Embodiment 7

This embodiment explains a combination of an insulating film and ananode formed on the insulating film.

FIG. 14A shows the measured value of the current efficiency η (cd/A) tothe luminance L (cd/m²) of the light-emitting element in which theinsulating film is formed of the silicon nitride oxide and in which theanode is formed using ITSO including the silicon oxide for 5 wt. % onthe insulating film. In order to compare, FIG. 14A also shows themeasured value of the current efficiency η (cd/A) to the luminance L(cd/m²) of the light-emitting element in which the insulating film isformed of the silicon nitride oxide and in which the anode is formedusing ITO on the insulating film.

The sample used in the measurement shown in FIG. 14A has a structure inwhich an insulating film using the silicon nitride oxide is formed onanother insulating film having a thickness of 0.8 μm including Si—O bondand Si—CH_(x) bond made of the material selected from the siloxanegroup. The insulating film using silicon nitride oxide is formed in 100nm thick by a CVD method.

As shown in FIG. 14A, it has been confirmed that the sample using theITSO as the anode has higher current efficiency than the sample usingthe ITO as the anode.

Next, FIG. 14B shows the measured value of the current efficiency η(cd/A) to the luminance L (cd/m²) of the light-emitting element in whichthe insulating film is formed of the silicon nitride and in which theanode is formed using ITSO including the silicon oxide for 5 wt. % onthe insulating film. In order to compare, FIG. 14B also shows themeasured value of the current efficiency η (cd/A) to the luminance L(cd/m²) of the light-emitting element in which the insulating film isformed of the silicon nitride and in which the anode is formed using ITOon the insulating film.

The sample used in the measurement shown in FIG. 14B has a structure inwhich an insulating film using the silicon nitride is formed on anotherinsulating film having a thickness of 0.8 μm including acrylic. Theinsulating film using silicon nitride is formed in 100 nm thick by asputtering method.

As shown in FIG. 14B, it has been confirmed that the sample using theITSO as the anode has higher current efficiency than the sample usingthe ITO as the anode as well as in FIG. 14A.

Next, FIG. 14C shows the measured value of the current efficiency η(cd/A) to the luminance L (cd/m²) of the light-emitting element in whichthe insulating film is formed of the silicon oxide and in which theanode is formed using ITSO including the silicon oxide for 5 wt. % onthe insulating film. In order to compare, FIG. 14C also shows themeasured value of the current efficiency η (cd/A) to the luminance L(cd/m²) of the light-emitting element in which the insulating film isformed of the silicon oxide and in which the anode is formed using ITOon the insulating film.

In the sample used in the measurement shown in FIG. 14C, the insulatingfilm is formed using the silicon oxide in 100 nm thick.

When FIGS. 14A, 14B, and 14C are compared, in the case of using ITSO asthe anode, it is understood that higher current efficiency can beobtained and higher internal quantum efficiency can be obtainedaccordingly when using the silicon nitride oxide or the silicon nitrideas the insulating film than when using the silicon oxide as theinsulating film.

Although FIGS. 14A to 14C show the case of the anode formed of a singlelayer of ITSO, it is considered that the internal quantum efficiency ofthe light-emitting device can be more enhanced by combining the abovestructure with the structure of the present invention. In other words,when the anode having the conductive light-transmitting oxide layer andthe barrier layer; the electroluminescent layer; and the cathode areformed sequentially on the insulating film including the silicon nitrideor the silicon nitride oxide, higher internal quantum efficiency can beobtained.

1. A method for manufacturing a semiconductor device, comprising thesteps of: forming a transistor including a semiconductor film; forming afirst insulating layer over the transistor; forming a first layer overthe first insulating layer, the first layer comprising a conductivelight-transmitting oxide material and silicon oxide; and removingmoisture adsorbed in the first layer.
 2. A method according to claim 1,further comprising the step of forming a second layer over the firstinsulating layer before forming the first layer, wherein the secondlayer comprises a conductive light-transmitting oxide material andsilicon oxide, and wherein a concentration of the silicon oxide in thefirst layer is higher than that of the second layer.
 3. A methodaccording to claim 2, wherein the first layer is formed by sputteringusing a first target containing the conductive light-transmitting oxidematerial and silicon oxide, and wherein the second layer is formed bysputtering using a second target containing the conductivelight-transmitting oxide material and silicon oxide.
 4. A methodaccording to claim 1, further comprising the steps of: forming anelectroluminescent layer over the first layer; and forming a conductivelayer over the electroluminescent layer.
 5. A method according to claim1, wherein the conductive light-transmitting oxide material is selectedfrom the group consisting of zinc oxide with gallium added, indium tinoxide, zinc oxide, and indium zinc oxide.
 6. A method according to claim1, wherein the transistor is a top gate transistor.
 7. A methodaccording to claim 1, wherein the semiconductor film of the transistoris any one of an amorphous semiconductor film, a micro-crystalsemiconductor film, and a poly-crystalline semiconductor film.
 8. Amethod for manufacturing a semiconductor device, comprising the stepsof: forming a transistor including a semiconductor film; forming a firstinsulating layer over the transistor; forming a first layer over thefirst insulating layer, the first layer comprising a conductivelight-transmitting oxide material and silicon oxide; and removingmoisture adsorbed in the first layer by performing a heat treatment attemperature ranging from 200° C. to 450° C.
 9. A method according toclaim 8, further comprising the step of forming a second layer over thefirst insulating layer before forming the first layer, wherein thesecond layer comprises a conductive light-transmitting oxide materialand silicon oxide, and wherein a concentration of the silicon oxide inthe first layer is higher than that of the second layer.
 10. A methodaccording to claim 9, wherein the first layer is formed by sputteringusing a first target containing the conductive light-transmitting oxidematerial and silicon oxide, and wherein the second layer is formed bysputtering using a second target containing the conductivelight-transmitting oxide material and silicon oxide.
 11. A methodaccording to claim 8, further comprising the steps of: forming anelectroluminescent layer over the first layer; and forming a conductivelayer over the electroluminescent layer.
 12. A method according to claim8, wherein the conductive light-transmitting oxide material is selectedfrom the group consisting of zinc oxide with gallium added, indium tinoxide, zinc oxide, and indium zinc oxide.
 13. A method according toclaim 8, wherein the transistor is a top gate transistor.
 14. A methodaccording to claim 8, wherein the semiconductor film of the transistoris any one of an amorphous semiconductor film, a micro-crystalsemiconductor film, and a poly-crystalline semiconductor film.
 15. Amethod according to claim 8, wherein the heat treatment is performedunder vacuum atmosphere.
 16. A method for manufacturing a semiconductordevice, comprising the steps of: forming a transistor including asemiconductor film; forming a first insulating layer over thetransistor; forming a first layer over the first insulating layer, thefirst layer comprising a conductive light-transmitting oxide materialand silicon oxide; and removing moisture adsorbed on the silicon oxideby performing a heat treatment at temperature ranging from 200° C. to450° C.
 17. A method according to claim 16, further comprising the stepof forming a second layer over the first insulating layer before formingthe first layer, wherein the second layer comprises a conductivelight-transmitting oxide material and silicon oxide, and wherein aconcentration of the silicon oxide in the first layer is higher thanthat of the second layer.
 18. A method according to claim 17, whereinthe first layer is formed by sputtering using a first target containingthe conductive light-transmitting oxide material and silicon oxide, andwherein the second layer is formed by sputtering using a second targetcontaining the conductive light-transmitting oxide material and siliconoxide.
 19. A method according to claim 16, further comprising the stepsof: forming an electroluminescent layer over the first layer; andforming a conductive layer over the electroluminescent layer.
 20. Amethod according to claim 16, wherein the conductive light-transmittingoxide material is selected from the group consisting of zinc oxide withgallium added, indium tin oxide, zinc oxide, and indium zinc oxide. 21.A method according to claim 16, wherein the transistor is a top gatetransistor.
 22. A method according to claim 16, wherein thesemiconductor film of the transistor is any one of an amorphoussemiconductor film, a micro-crystal semiconductor film, and apoly-crystalline semiconductor film.
 23. A method according to claim 16,wherein the heat treatment is performed under vacuum atmosphere.
 24. Amethod for manufacturing a light-emitting device, comprising the stepsof: forming a first conductive layer over a substrate, the firstconductive layer comprising a first layer including a conductivelight-transmitting oxide material and silicon oxide; removing moistureadsorbed in the first layer; forming an electroluminescent layer overthe first conductive layer; and forming a second conductive layer overthe electroluminescent layer.
 25. A method according to claim 24,wherein the first conductive layer further comprises a second layerincluding a conductive light-transmitting oxide material and siliconoxide, and wherein a concentration of the silicon oxide in the firstlayer is higher than that of the second layer.
 26. A method according toclaim 25, wherein the first layer is formed by sputtering using a firsttarget containing the conductive light-transmitting oxide material andsilicon oxide, and wherein the second layer is formed by sputteringusing a second target containing the conductive light-transmitting oxidematerial and silicon oxide.
 27. A method according to claim 24, whereinthe conductive light-transmitting oxide material is selected from thegroup consisting of zinc oxide with gallium added, indium tin oxide,zinc oxide, and indium zinc oxide.
 28. A method according to claim 24,wherein the step of removing the moisture is before the step of formingthe electroluminescent layer.
 29. A method according to claim 24,wherein the first conductive layer is a cathode.
 30. A method formanufacturing a light-emitting device, comprising the steps of: forminga first conductive layer over a substrate, the first conductive layercomprising a first layer including a conductive light-transmitting oxidematerial and silicon oxide; removing moisture adsorbed in the firstlayer by performing a heat treatment at temperature ranging from 200° C.to 450° C.; forming an electroluminescent layer over the firstconductive layer; and forming an second conductive layer over theelectroluminescent layer
 31. A method according to claim 30, wherein thefirst conductive layer further comprises a second layer including aconductive light-transmitting oxide material and silicon oxide, andwherein a concentration of the silicon oxide in the first layer ishigher than that of the second layer.
 32. A method according to claim31, wherein the first layer is formed by sputtering using a first targetcontaining the conductive light-transmitting oxide material and siliconoxide, and wherein the second layer is formed by sputtering using asecond target containing the conductive light-transmitting oxidematerial and silicon oxide.
 33. A method according to claim 30, whereinthe conductive light-transmitting oxide material is selected from thegroup consisting of zinc oxide with gallium added, indium tin oxide,zinc oxide, and indium zinc oxide.
 34. A method according to claim 30,wherein the step of removing the moisture is before the step of formingthe electroluminescent layer.
 35. A method according to claim 30,wherein the heat treatment is performed under vacuum atmosphere.
 36. Amethod according to claim 30, wherein the first conductive layer is acathode.
 37. A method for manufacturing a light-emitting device,comprising the steps of: forming a first conductive layer over asubstrate, the first conductive layer comprising a first layer includinga conductive light-transmitting oxide material and silicon oxide;removing moisture adsorbed on the silicon oxide by performing a heattreatment at temperature ranging from 200° C. to 450° C.; forming anelectroluminescent layer over the first conductive layer; and forming ansecond conductive layer over the electroluminescent layer.
 38. A methodaccording to claim 37, wherein the first conductive layer furthercomprises a second layer including a conductive light-transmitting oxidematerial and silicon oxide, and wherein a concentration of the siliconoxide in the first layer is higher than that of the second layer.
 39. Amethod according to claim 38, wherein the first layer is formed bysputtering using a first target containing the conductivelight-transmitting oxide material and silicon oxide, and wherein thesecond layer is formed by sputtering using a second target containingthe conductive light-transmitting oxide material and silicon oxide. 40.A method according to claim 37, wherein the conductivelight-transmitting oxide material is selected from the group consistingof zinc oxide with gallium added, indium tin oxide, zinc oxide, andindium zinc oxide.
 41. A method according to claim 37, wherein the stepof removing the moisture is before the step of forming theelectroluminescent layer.
 42. A method according to claim 37, whereinthe heat treatment is performed under vacuum atmosphere.
 43. A methodaccording to claim 37, wherein the first conductive layer is a cathode.